The present invention relates to an improvement to a diffractive display (reflective or transmissive) wherein each pixel exhibits a full range of diffracted wavelengths (e.g., full range of colors) by a novel diffractive technique.
The art is replete in proposing graphics displays which utilize, for example, bimorph elements or, simply, bimorphs, or equivalents. A bimorph is a device manufactured with two strips of piezoelectric film which are fastened together and which have electrodes allowing electrical fields of the proper polarity to be applied to the film to cause an electrostrictive effect to occur. Such electrostrictive effect can be an in-plane elongation or contraction, or an out-of-plane deflection of one end of the film when the opposite end is secured.
U.S. Pat. No. 4,331,972 proposes a light valve comprising a pair of elements of transparent material, each comprising a diffraction grating of light periodicity facing each other with parallel grating lines. Such light valve is termed a bigrate in this patent. The transmission of light through the bigrate will depend on the relative position of the pair of gratings in the direction perpendicular to the grating lines. One of the gratings may be embossed on a bimorph film of polyvinylidene fluoride and moved by the application of a voltage thereto. One strip, then, may be moved relative to the other in response to an electrical signal to control the zero diffraction or the light transmission from no transmission to full transmission, or any desired intermediate transmission. Three different superimposed bigrated light valves are used for achieving the three different colors required for a color display, viz., cyan, magenta, and yellow.
U.S. Pat. No. 5,067,829 proposes to steer light beams by passing the light beams through optically transparent elastic material which are bent under the application of a voltage which bending or deformation causes the change in the angle at which the light beam intercepts the surfaces of the optically transparent layers.
U.S. Pat. No. 5,052,777 utilizes a bimorph as a shutter to pass or block light coupling therethrough. Such bimorph shutters permit light, such as transmitted through optical fibers, to be coupled through the bimorph light valves to an observer for generating graphic displays.
U.S. Pat. No. 4,274,101 discloses a laser recorder that utilizes a piezoelectric bimorph focal length vibrator.
U.S. Pat. No. 5,126,836 proposes a television display wherein a white light source emits a beam onto a plurality of dichroic mirrors which split the beam into three beams of primary colors, then reflects the primary beams onto three deformable reflective surfaces which may be piezoelectric crystals, which again reflect the beams through slits in a non-reflective surface, thereby modulating the intensity of the beams. U.S. Pat. No. 4,415,228 also proposes a bimorph light valve, as does U.S. Pat. No. 4,234,245.
Additional proposals include Stein, et al, “A Display Based on Switchable Zero Order Diffraction Grating Light Valves”, Advances in Display Technology V, SPI vol. 526, 105-112 (1985), which propose a flat panel display which utilizes a matrix of line addressable light valves back-lighted with a partially collimated source. The basic pixel element of the display is an optical switch based on the zero order of diffraction by two aligned transmission phase gratings. The transmission of light is modulated by mechanically displacing one grating with respect to the other by one-half of the grating. A bimorph is used for this purpose.
Finally, another proposal is by Gale, et al., “Diffractive Diffusers for Display Application”, Current Developments in Optical Engineering and Diffraction Phenomena, SPIE vol. 679, 165-168 (1986), which propose diffractive optical diffusers for display applications wherein the diffusers can be fabricated by laser beam writing techniques.
The foregoing techniques function to some degree to provide graphic displays; however, a much improved technique for creating such displays is disclosed in U.S. Pat. No. 5,613,022, by Odhner, et al., entitled “Diffractive Display and Method Utilizing Reflective or Transmissive Light Yielding Single Pixel Full Color Capability,” issued Mar. 18, 1997. Through movement of a diffraction grating, this technique can be used to create graphic displays, each pixel of the display being capable of full color. A diffuser panel or image surface can be illuminated by the pixel for enhancing viewing of the display by an observer.
While this diffractive technique represents an advancement in the field of graphics displays, there still exists a real need in the art for additional ways to implement this approach in order to make such diffractive displays economical and practical, especially when produced in large volume.